Once a technology is ready to be tested at pilot or commercial scale, the cost of building a test facility becomes significant -- often beyond the funding provided for any one project. It then becomes critical to test the technology at a pre-existing facility willing to test experimental technologies. Not surprisingly, most commercial facilities are hesitant to interfere with their operations to experiment, but others, with a view towards the future, welcome promising technologies. Below is a list of major partner test sites that actively host DOE supported research activities. Many of the test sites were built with DOE support, but many were not. Some are commercial, and were designed to perform experimental work. All play an important role in developing technologies with minimal expense to the project, and to the U.S. taxpayer.